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		Implementing the Main Program
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            <h2 class="title" style="clear: both"><a id="implementingmain"></a>
		Implementing the Main Program
	</h2>
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      <p>
    The main program opens the environment and databases, stores and retrieves
	objects within a transaction, and finally closes the environment
	databases. This section describes the main program shell, and the
	next section describes how to run transactions for storing and
	retrieving objects.
</p>
      <p>
    The <code class="classname">Sample</code> class contains the main program. The skeleton
	for the <code class="classname">Sample</code> class follows.
</p>
      <a id="cb_java_sample"></a>
      <pre class="programlisting"><strong class="userinput"><code>import com.sleepycat.db.DatabaseException;
import java.io.FileNotFoundException;

public class Sample
{
    private SampleDatabase db;
    private SampleViews views;

    public static void main(String args)
    {
    }

    private Sample(String homeDir)
        throws DatabaseException, FileNotFoundException
    {
    }

    private void close()
        throws DatabaseException
    {
    }

    private void run()
        throws Exception
    {
    }
}</code></strong> </pre>
      <p>
    The main program uses the <code class="classname">SampleDatabase</code> and
	<code class="classname">SampleViews</code> classes that were described in the preceding
	sections. The <code class="methodname">main</code> method will create an instance of the
	<code class="classname">Sample</code> class, and call its <code class="methodname">run()</code> and <code class="methodname">close()</code>
	methods.
    
</p>
      <p>
    The following statements parse the program's command line
	arguments.
</p>
      <a id="cb_main"></a>
      <pre class="programlisting">    public static void main(String[] args)
    {
<strong class="userinput"><code>        System.out.println("\nRunning sample: " + Sample.class);
        String homeDir = "./tmp";
        for (int i = 0; i &lt; args.length; i += 1)
        {
            String arg = args[i];
            if (args[i].equals("-h") &amp;&amp; i &lt; args.length - 1)
            {
                i += 1;
                homeDir = args[i];
            }
            else
            {
                System.err.println("Usage:\n java " + 
                                   Sample.class.getName() +
                                  "\n  [-h &lt;home-directory&gt;]");
                System.exit(2);
            }
        }</code></strong>
        ...
    } </pre>
      <p>
    The usage command is:
</p>
      <pre class="programlisting"><strong class="userinput"><code>java com.sleepycat.examples.bdb.shipment.basic.Sample
     [-h &lt;home-directory&gt; ]</code></strong> </pre>
      <p>
    The <code class="literal">-h</code> command is used to set the <code class="filename">homeDir</code>
	variable, which will later be passed to the <code class="methodname">SampleDatabase()</code>
	constructor. Normally all Berkeley DB programs should provide a way
	to configure their database environment home directory.
</p>
      <p>
    The default for the home directory is <code class="filename">./tmp</code> — the tmp
	subdirectory of the current directory where the sample is run. The
	home directory must exist before running the sample. To re-create
	the sample database from scratch, delete all files in the home
	directory before running the sample.
</p>
      <p>
    The home directory was described previously in
    <a class="xref" href="opendbenvironment.html" title="Opening and Closing the Database Environment">
		Opening and Closing the Database Environment
	</a>.
</p>
      <p>
    Of course, the command line arguments shown are only examples
	and a real-life application may use different techniques for
	configuring these options.
    
</p>
      <p>
    The following statements create an instance of the <code class="classname">Sample</code>
	class and call its <code class="methodname">run()</code> and <code class="methodname">close()</code> methods.
</p>
      <a id="cb_main2"></a>
      <pre class="programlisting">    public static void main(String args)
    {
        ...
<strong class="userinput"><code>        Sample sample = null;
        try
        {
            sample = new Sample(homeDir);
            sample.run();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (sample != null)
            {
                try
                {
                    sample.close();
                }
                catch (Exception e)
                {
                    System.err.println("Exception during database close:");
                    e.printStackTrace();
                }
            }
        }</code></strong>
    } </pre>
      <p>
    The <code class="methodname">Sample()</code> constructor will open the environment and
	databases, and the <code class="methodname">run()</code> method will run transactions for
	storing and retrieving objects. If either of these throws an
	exception, then the program was unable to run and should normally
	terminate. (Transaction retries are handled at a lower level and
	will be described later.) The first <code class="literal">catch</code> statement handles
	such exceptions.
</p>
      <p>
    The <code class="literal">finally</code> statement is used to call the <code class="methodname">close()</code>
	method since an attempt should always be made to close the environment and
    databases
	cleanly. If an exception is thrown during close and a prior
	exception occurred above, then the exception during close is likely
	a side effect of the prior exception.
</p>
      <p>
    The <code class="methodname">Sample()</code> constructor creates the <code class="literal">SampleDatabase</code>
	and <code class="classname">SampleViews</code> objects.
</p>
      <a id="cb_sample"></a>
      <pre class="programlisting">    private Sample(String homeDir)
        throws DatabaseException, FileNotFoundException
    {
<strong class="userinput"><code>        db = new SampleDatabase(homeDir);
        views = new SampleViews(db);</code></strong>
    } </pre>
      <p>
    Recall that creating the <code class="classname">SampleDatabase</code> object will open
	the environment and all databases.
</p>
      <p>
    To close the database the <code class="methodname">Sample.close()</code> method simply
	calls <code class="methodname">SampleDatabase.close()</code>.
</p>
      <a id="cb_sample-close"></a>
      <pre class="programlisting">     private void close()
        throws DatabaseException
    {
<strong class="userinput"><code>        db.close();</code></strong>
    } </pre>
      <p>
    The <code class="methodname">run()</code> method is described in the next section.
</p>
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